1a. Objectives (from AD-416)
As the number and severity of produce-associated gastroenteritis outbreaks increase, we are coming to recognize that we know little about the ecology of Salmonella and enterovirulent E. coli outside of their animal hosts. It is clear that these human pathogens can contaminate fruits, vegetables, nuts and sprouts, at pre- and/or post-harvest production stages. How these bacteria infect, colonize, and persist within plants and evade reasonably rigorous surface sanitation is much less certain. Some of the ongoing debate focuses on the question of whether plants are true alternate hosts for non-typhoidal S. enterica or E. coli O157:H7, or whether plants are simply matrices where these organisms transiently persist in a resting state. If enteric pathogens enter into a relationship with a plant host as a part of their normal life cycle, then it is important to define differences in genetic and regulatory programs that the enterics require for the two alternating lifestyles (animal pathogen vs plant commensal) and how they might impact important developmental processes of the plant such as fruit ripening. Our goal is to determine what genes and regulatory programs are needed by Salmonella to inhabit tomato plants, and to examine the effects of plant host genotype, developmental stage and fertilization regime on external and internal colonization by Salmonella in addition to its effects on ripening and quality parameters that may provide diagnostic markers. The information obtained may very well have future valuable practical applications in modifying production practices to reduce outbreaks of produce-associated gastroenteritis.

1b. Approach (from AD-416)
Some tomato cultivars are readily colonized by Salmonella while others are not or are greatly reduced in bacterial titer. To establish the basis of the “resistance” of tomato cultivars to Salmonella, we will need to delineate signal transduction mechanisms and responses of the plant host to colonization by this human enteric pathogen. We propose transcriptome characterization of tomato responses to Salmonella to achieve this goal. Specifically, we will perform transcriptome profiling of tomato fruits colonized with S.e. sv Typhimurium 14028 (vs. control fruit) to identify differentially regulated genes that reflect processes and pathways contributing to, or influenced by, colonization and reflect impacts on fruit ripening or quality.

3. Progress Report
As the number and severity of produce-associated gastrointestinal disease outbreaks increase, we are coming to recognize that we know little about the ecology of human disease causing Salmonella and E. coli bacteria outside of their animal hosts. It is clear that these human pathogens can contaminate fruits, vegetables, nuts and sprouts, at pre- and/or post-harvest production stages. How they infect, colonize, and persist within plants and evade reasonably rigorous surface sanitation is much less certain. This project is based on our discovery that in tomatoes of some cultivars, Salmonella reached populations that differ by 100-1,000 fold, suggesting that plant genotype and genetics can impact the ability of these pathogens to colonize produce prior to causing human disease. Understanding the genetic and physiological basis of this apparent “resistance” is the goal of this proposal with the longer-term objective trained toward developing crop varieties that will assist in the fight against these food bourn diseases. The project has recently been initiated (February, 2011) and to date we have been optimizing strand-specific RNA-seq and associated methodologies for developing the transcriptome data component that our laboratory will handle. This project is in all respects on schedule and on budget. Phone conversations and email are used on a frequent basis as needed to address questions, technical problems, or to plan next steps when milestones are reached. BI-annual meeting are anticipated as the project continues.